LMS-Based Pediatric Reference Values for Parameters of Phosphate Homeostasis in the HARP Cohort

Context: The assessment of phosphate homeostasis in children is challenging due to the marked changes in laboratory parameters during growth and development, and the lack of adequate reference values.

Objective: To develop Lambda-Mu-Sigma (LMS)-based continuous pediatric reference percentiles for 7 key laboratory parameters of phosphate homeostasis.

Methods: This cross-sectional, single-center study, the HAnnover Reference values for Pediatrics (HARP) study, included 455 children aged 0.1-18 years (254 boys) from outpatient hospital clinics and a secondary school program. Main outcome measures were LMS-based continuous reference percentiles for serum phosphate, plasma intact fibroblast growth factor 23 (iFGF23), and its cofactor soluble Klotho (sKlotho), tubular maximum phosphate reabsorption per glomerular filtration rate (TmP/GFR), fractional tubular reabsorption of phosphate (TRP), and urinary calcium/creatinine (Ca/Crea) and phosphate/creatinine (Pi/Crea) ratios.

Results: LMS-based percentiles and z-scores were established for 7 key laboratory parameters of phosphate homeostasis, which were all found to be age-dependent. Serum phosphate, TmP/GFR, and sKlotho associated with sex. Serum phosphate, TmP/GFR, and urinary Ca/Crea and Pi/Crea levels were highest in infancy and declined until age 18 years, while phosphate and TmP/GFR values reached adult levels earlier in girls compared to boys. iFGF23 concentrations are highest in infancy and fall to a stable plateau by 4 years of age, while sKlotho peaks during adolescence.

Conclusion: This is the first report of LMS-based continuous pediatric reference percentiles for key laboratory parameters of phosphate homeostasis that allow calculation of standardized patient z-scores to facilitate test result interpretation in children and adolescents.